Alkenyltins

The tin-to-lithium exchange in alkenyltins is characterized by the preservation of the alkene stereochemistry and is compatible with several functionalities on the alkene moiety such as amino, hydroxyl and ester groups. The transmetallation of functionalized vinyltins has found an application in the synthesis of complex molecules such as unsaturated fatty acids [362], prostaglandin side-chain [363], various antibiotics ]364] and a biotoxin [365]. 

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The reaction of alkenyl iodides or triflates, alkenylstannanes, and CO affords divinyl ketones[397,398]. Thus the capnellene skeleton 538 has been synthesized by the carbonylation of the cyclopentenyl triflate 536 with the alkenyltin 537[392], The macrocyclic divinyl ketone 540 has been prepared in a moderate yield by the carbonylative cyclization of 539[399]. 

Various organotin reagents react with acyl and aroyl halides under mild conditions without decarbonylation to give carbonyl compounds[390,39l]. Alkyl- or alkenyltin reagents react with acyl and aroyl chlorides to give ketones[548.733,734]. One example is the preparation of the a,/3-dnsaturated 7-keto esters 860 and 861, carried out under a CO atmosphere[735]. The reaction has been applied intramolecularly to the synthesis of the macrocyclic keto... 

By regiospecific [4+2] cycloadditions of functional alkenyltin derivatives with dienes such as 1,3-butadiene, 2,3-dimethyl-l,3-butadiene or 1-substituted 1,3-butadienes, polyfunctional cyclic vinyltin compounds 80 are obtained. 

SnCl2 reacts with triphenylethenyllithium Li(CPh=CPh2) in Et20-w-hexane-THF to yield an alkenyltin(II) derivative which, subsequently treated with butyl bromide, yields a mixed alkyltin halide362 ... 

In organic synthetic procedures, alkenyltin compounds are often prepared with a view to subsequent transmetalla-tion with lithium, or to the Stille coupling reaction with a palladium catalyst (Equations (70) and (71)). 

In addition to alkenylboron compounds, alkenylalane, alkenylzirconium, alkenyltin, alkenyl copper, and alkenylmagneslura reagents are reported to undergo a related alkenyl-alkenyl coupling reaction to give l,3-a1kad1enes. 

Tetrahydronaphthalen-2-yl)-3-buten-2-ol [Coupling between an alkenyltin and an aryl perfluorobutanesulfonate using copper(l) and lithium chloride] [69]. 

Addition of in situ generated trichlorostannane to propiolic acid derivatives furnishes the corresponding j9-trichlorostannylacrylic acid derivatives (Scheme 33) [144]. The procedure provides an access to trialkyltin free alkenyltin reagents. 

Regio- and stereoselective stannylcupration of terminal alkynes provides the corresponding (R)-l-stannylalkenes, exclusively [62,150,153-167]. Methylation of the intermediary alkenylcopper species provides the corresponding trisubsti-tuted alkenyltin reagent, stereoselectively [168]. Carbostannylation of alkynes offers another sophisticated possibility [32,169-179]. Hetero-atom assisted lithi-ation and subsequent stannylation of alkene also provides the corresponding alkenyltins (Scheme 36) [180]. 

The use of 3,3-tributylstannyl-l-siloxy-l-propene leads to stereodefined preparation of a variety of polyfimctionalized 1-alkenyltin reagents, of which some examples are depicted in Scheme 37 [181-183]. 

Palladium-catalyzed cross coupling between alkenyl halides or triflates (Scheme 38) [184] and ditin affords the corresponding alkenyltin stereospecifi-cally with retention of configuration (Scheme 39) [185]. 

A guiding mechanism for this reaction is analogous to the direct coupling as shown in Scheme 5, except CO insertion that takes place probably between the oxidative-addtion step and the transmetallation step. The reaction of alkenyl iodides with alkenyltins takes place under neutral and mild conditions (40-50°, under 1-3 atm CO in THF) (Scheme 76) [288]. 

Table 2. Stereospecific carbonylative cross coupling of a (Z)-alkenyltin...

The main feature of tin to hthium exchange is the preservation of the alkene stereochemistry, which was already demonstrated in 1964 . In conjunction with the easy access to stereodefined alkenyltins, this feature has been extensively exploited for synthetic purposes such as the construction of prostaglandins side chains and unsaturated fatty acids ° ° , the syntheses of a macrocyclic lactone , brefeldin cerulenin... 

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